renato ambrósio jr., md, phd* diogo l. caldas, md isaac c. ramos, md rodrigo t. santos, md

© R. Ambrósio Jr, MD, PhD © R. Ambrósio Jr, MD, PhD - 2011- 2011

R. Ambrósio R. Ambrósio JrJr&&

Rio de Rio de Janeiro Janeiro Corneal Corneal

Tomography Tomography andand

BiomechanicsBiomechanicsStudy GroupStudy Group

Corneal Biomechanical Assessment using Dynamic

Ultra High-Speed Scheimpflug Technology Non-Contact

Tonometry (UHS-ST NCT): Preliminary ResultsRenato Ambrósio Jr., MD, PhD*

Diogo L. Caldas, MD Isaac C. Ramos, MD

Rodrigo T. Santos, MDLeonardo N. Pimentel, MD

Cynthia Roberts, PhD*Michael W. Belin, MD*

Dr. Ambrósio & Dr. Belin are consultants for Oculus Optikgeräte GmbH

(Wetzlar, Germany) and have received research funding and travel reimbursements






Introduction: Evolution on Corneal

Propedeutics “Propedeutics” refers (in Medicine) to the

collection of data about a patient by observations and examinations.

Advances are recognized on the ability for architecture or goemetrical characterization of the cornea

Keratometry, Keratoscopy, Videokeratography, Corneal Topography, Corneal Tomography






Corneal Biomechanics: Relevance

From Geometrical and Optical understanding, the next step is biological evaluation: healing response and biomechanics Ectasia mysteries* in Refractive Surgery had

highlight the need for corneal biomechanical understanding(*ie: cases with no risk factors that develop ectasia after LASIK) Also to Customize Refractive Corneal

Treatments; correctly measure IOP (intraocular pressure) and to possibly predict glaucoma risk Corneal biomechanical evaluations were limited

to in vitro studies and to mathematical finite element models until the Ocular Response Analyzer (ORA-Reichert, Depew) in 2005 New techniques are under development for

evaluating biomechanics This e-Poster presents a new system – The

Corvis ST (Oculus, Wetzlar, Germany) with preliminary clinical results.






Ultra High-Speed (UHS ST) Scheimpflug Technology takes 4,330 frames/sec with 8mm horizontal coverage Monitors corneal deformation response to

a symmetrically metered air pulse

The Oculus Corvis ST

1. Natural; (Ingoing Phase) 2. First Applanation (1st A) Momentum; 3 and 4. Ingoing Concavity Phase; 5. Highest Concavity Momentum; 6. Oscillation Period; (Outgoing Phase); 7. Second Applanation (2nd A) Momentum; 8.

After Second Applanation; 9. Natural Back1st Applanation, Highest Concavity and 2nd Applanation: Time and Length; Maximum Deformation; Maximum Velocity In and Out; Thickness






Corvis ST: First Studies Experiment involving contact lenses mounted on

an artifical pressurized chamber (Caldas et al., ePostar ASCRS 2011) found that the deformation response is influenced by lens properties and chamber pressure. The inspection of the actual deformation process

details corneal characterization, which has a potential for distinguishing normal (A, B) and keratoconus (C, D) corneas (see video* (see video* PosterASCRS2011_clip_RAmbrosio).PosterASCRS2011_clip_RAmbrosio).

Natural and Highest Deformation Momentum in a Normal (A, B) and a Keratoconic (C, D) Cornea






Corvis ST: Clinical Parameters

IOP: is the NCT measurement based on the 1st Applanation1st A-time: is the time from starting

until the first applanation HC-time: time from starting until

Highest Concavity is reached 2nd A-time: time from starting

until the second applanation 1st A length: cord length of the first

applanation 2nd A length: cord length of the second

applanation Def Amp: maximum amplitude at the apex

(highest concavity) W-Dist: distance of the two “knee’s” at highest

concavity (HC) Curvature Rad HC: central concave curvature

at HC Curvature Rad normal: initial central convex

curvatureVin: corneal speed during the first applanation

momentVout: corneal speed during the second

applanation moment






0 20 40 60 80 100

0

20

40

60

80

100

100-Specificity

Sen

sitiv

ity

1st A Length(max):1st A Time:2nd A Length(max):2nd A Time:Curv, Rad, HC:Def,Amp,(max):

The Corvis ST was utilized to assess corneal deformation response in one eye from 71 keratoconic patients and in one eye from 178 normal patients. Clinical diagnosis was based on the complete eye

exam, Placido-disk based corneal topography and Pentacam Corneal Tomography.

Clinical Study

Wilcoon Rank Sum (Mann- Whitney Test)

IOP: < 0.00011st A Time: < 0.00012nd A Time: 0.0006

1st A Length(max): 0.00372nd A Length(max): 0.0008Curv. Rad. Normal: 0.4126

Curv. Rad. HC: < 0.0001Pachy Apex: < 0.0001

W-Dist.: 0.0191Def.Amp.(max): < 0.0001

Vin: < 0.0001Vout: 0.0001

Statistically significant distributions for all parameters (Mann-Whitney, p<0.05), but with significant overlap and AUC(area under the ROC curves) between 0.673 and 0.852






Corvis Combo1: combined parameter

Joint work with “Instituto de Computação” at UFAL (Universidade Federal de Alagoas*) to develop a combined parameter (Corvis Combo1) based on a linear regression analysis, considering the effects of IOP on deformation response parameters 0.033 * IOP - 0.004 * Pachy Apex - 0.448 * 1st A Time - 0.049 * HC Time + 0.093 * 2nd A Time + 0.026 * 1st A Length(max) - 0.105 * 2nd A Length(max) + 0.208 * Def Amp (max) - 0.619 * W-Dist - 0.021 * Curv, Rad, HC - 0.101 * Curv, Rad, Normal - 0.525 * Vin - 0.166 *

Vout + 7.952

combo1

0 20 40 60 80 100

0

20

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60

80

100

100-Specificity

Sen

sitiv

ity

Sensitivity: 87,3 Specificity: 89,3 Criterion : >0,2527

N KC

Ave-

0,008010,50682

9

SD0,21834

8 0,26691

* Prof. Aydano P. Machado & J. M. Lyra, MD, PhD






0 20 40 60 80 100

0

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Sen

sitiv

ity

1st A Time:Def,Amp,(max):Pachy Apex:Curv, Rad, HC:Curv, Rad, Normal:combo1

AUC SE a 95% CI b 1st_A_Time_ 0,802 0,0313 0,747 to 0,850

Def_Amp__max__ 0,749 0,0355 0,691 to 0,802Pachy_Apex_ 0,852 0,0265 0,801 to 0,893

Curv__Rad__HC_ 0,852 0,0290 0,802 to 0,894Curv__Rad__Norm

al_ 0,810 0,0329 0,755 to 0,857CorvisST Combo1 0,931 0,0191 0,892 to 0,959

a DeLong et al., 1988 b Binomial exact

The Corvis ST Combo1 performed statistically better (p<0.05; Pairwise ROC comparisons) than the individual parameters from the Corvis ST to distinguish 71 keratoconic eyes and 178 normal eyes (one eye per patient included) This approach has been complementary to

enhance the diagnosis of ectasia susceptibility.

Clinical Study

0 20 40 60 80 100

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20

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1st A Time:Def,Amp,(max):Pachy Apex:Curv, Rad, HC:Curv, Rad, Normal:combo1






There were very significant correlations (Spearman, p<0.001) between IOP and 1st Applanation Time (rho=0.94), 2nd Applanation Time (rho=-0.73), Deformation Amplitude (rho=-0.80), W-Dist (rho=-0.66), Curv Rad HC (rho=0.45), Vin (rho=-0.49), Vout (0.38) and Combo1 (rho=-0.44)There was a significant correlation (Spearman, p<0.01)

between Pachymetry at the Apex and IOP (rho=0.37), 1st Applanation Time (rho=0.4 ) and Lengh (rho=-0.18 ), W-Dist (rho=-0.25), Curv Rad HC (rho=0.48), Vout (rho=0.3), and Combo1 (rho=-0.64) There was a weak correlation between age and HC Time

(Spearman, p=0.0039; rho=0.22)

Clinical Correlations






Enhanced Screening for Ectasia Susceptibility

Biomechanical data from Corvis ST enhances the Biomechanical data from Corvis ST enhances the capability to detect very mild cases of ectasia and also capability to detect very mild cases of ectasia and also help to characterize stable cases with asymmetric bow help to characterize stable cases with asymmetric bow tie and inferior steepening (ABT/IS).tie and inferior steepening (ABT/IS). 26 eyes diagnosed as Forme Fruste Keratoconus 26 eyes diagnosed as Forme Fruste Keratoconus

(FFKC), with normal front curvature map while the (FFKC), with normal front curvature map while the fellow eye has keratoconus were examined.fellow eye has keratoconus were examined. 25 eyes with ABT/IS but with no other clinical or 25 eyes with ABT/IS but with no other clinical or

tomographic sign of ectasia were examined. tomographic sign of ectasia were examined. Combo1 21/26 (80%) eyes with FFKC >0.21 24/178 (13%) normal eyes <0.21 8/25 (32%) ABT/IS cases <0.21

Kruskall-Wallis Test Normal KC FFKC ABT/IS

Normal <0.05 <0.05 NS

KC NS <0.05

FFKC <0.05

N FFK1 KC ABT

Ave

-0,0080

10,3455

290,5068

290,1337

45

SD0,2183

480,1960

430,2669

10,1816

24 171 26 71 25

see video* see video* PosterASCRS2011_clip_RAmbrosioPosterASCRS2011_clip_RAmbrosio






Combo 1=0.16Combo 1=0.16 Combo 1=0.31Combo 1=0.31

The inspection of corneal deformation during NCT enables biomechanical characterization The deformation is severely influenced by IOP Combo1 from Corvis ST provides clinically

relevant parameter to enhance sensitivity and specificity to detect ectasia.

Corvis ST: Conclusions

ABT with no Ectasia (A,B) x FFKC (C, D) This approach This approach is is complementary complementary to Corneal to Corneal Tomography Tomography with the with the Pentacam for Pentacam for screening screening refractive refractive candidatescandidates

renato ambrósio jr., md, phd* diogo l. caldas, md isaac c. ramos, md rodrigo t. santos, md

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